An electrical fan usually includes a frame, a bearing support formed at a middle of the frame, a stator disposed around the bearing support, and a rotor rotatably mounted surrounding the stator. The bearing support is for receiving a bearing therein. The bearing rotatably supports a rotor shaft which is connected with the rotor. The bearing support is usually made of plastic, and includes a central tube for positioning the stator. The heat generated by electronic components increases as the power of the electronic components grows. In order to dissipate this heat, the fan will need high rotating speed to drive the rotor to generate more airflow, which results in the increase of the heat generated by the motor of the fan consisting of the stator, rotor, bearing support, bearing and rotor shaft. With the accumulation of the heat, the plastic tube of the motor will become soften and deformed when the temperature of the motor rises beyond a predetermined value. This leads the fan to become vibrant and noisy when it works, and reduces the life of the fan.
In order to solve this problem, another fan frame having better heat-resistant and heat-conductivity ability has been proposed. The frame includes a plastic bracket and a metal tube connected with the bracket. Because the metal tube has good heat-resistant ability, it will not unduly deform when the temperature increases. The metal tube can also dissipate the heat generated by the motor to the environment because of its good heat-conductivity, resulting in the temperature of the fan motor stayed at a low level.
The metal tube is usually molded with the plastic bracket. To strengthen the connection of the metal tube and the plastic bracket, an outer connecting surface of the metal tube is formed with grooves or indents. However, forming processes of the grooves or the indents on the metal tube are complicated and therefore costly.
In addition, to precisely position the bearing in the metal tube, an inner surface of the metal tube needs to be processed to obtain an acceptably precise hole size. This also increases the cost of the metal tube. Further, once the tube is determined, it only fits bearings of a specific size. If the size of the bearings is changed, the metal tube cannot be used. What is needed, therefore, is an improved fan frame for a heat dissipating fan.